Also, another way to achieve this is would be after completely a lap using the highest speed achieve on the lap.
This could be done dynamically lap by lap to check highest speed but for something like a fan controller the data does not have to be spot on. Nobody is going to notice a small amount of discrepancy. Anything is better than forgetting you have change vehicles and have the fans running at 100% whilst you are only at 20% of your max speed.
I think this "Automatic" function would certainly help with sales of the Fan Controller